1. Field of the Invention
This invention relates to circuit breakers for protecting electric power circuits. More particularly, it relates to circuit breakers with a set of secondary contacts, which are controllable through an operator, such as a magnetically latchable solenoid.
2. Background Information
Circuit breakers used in residential and light commercial applications are commonly referred to as miniature circuit breakers because of their limited size. Such circuit breakers typically have a pair of separable contacts opened and closed by a spring biased operating mechanism. A thermal-magnetic trip device actuates the operating mechanism to open the separable contacts in response to persistent overcurrent conditions and to short circuits. Usually, circuit breakers of this type for multiple circuits within a residence or commercial structure are mounted together within a load center which may be located in a basement or other remote location. In some applications, it has been found convenient to use the circuit breakers for other purposes than just protection, for instance, for load shedding. It is desirable to be able to perform this function remotely, and even automatically, such as under the control of a computer. However, the spring biased operating mechanisms are designed for manual reclosure and are not easily adapted for reclosing remotely. In any event, such operating mechanisms are not designed for repeated operation over an extended period of time.
U.S. Pat. Nos. 5,301,083 and 5,373,411 describe a remotely operated circuit breaker, which introduces a second pair of contacts in series with the main separable contacts. The main contacts still interrupt the overcurrent, while the secondary contacts perform the discretionary switching operations. The secondary contacts are controlled by a solenoid, which is spring biased to close the contacts. The solenoid has two coils, an opening coil and a holding coil. Initially, both coils are energized to open the contacts. Power to the opening coil is then turned off, and only the holding coil remains energized. Thus, continuous power is required to keep the main contacts open. When power to the holding relay is terminated, the spring recloses the secondary contacts.
U.S. Pat. No. 6,259,339 discloses a remotely operated circuit breaker, which introduces secondary contacts in series with main separable contacts. The secondary contacts are controlled by a solenoid, which has two coils, a first (or close) coil and a second (or open) coil. The coils are concentrically wound on a steel core supported by a steel frame. A plunger moves rectilinearly within the coils. A permanent magnet is seated between the steel core and the steel frame. When the close coil is energized, a magnetic field is produced which counteracts the magnetic field produced by the permanent magnet. A spring then pushes the contact arm closed. The secondary contacts are maintained in the closed state by a spring. When it is desired to open the secondary contacts, the open coil is energized which lifts the plunger to open the secondary contacts. With the plunger in the full upward position, it contacts the steel core and is retained in this second position by the permanent magnet. Subsequently, when the close coil is energized, the magnetic field generated is stronger than the field of the permanent magnet and therefore overrides the latter and moves the plunger back to the closed position.
There is room for improvement in externally operated circuit breakers.
This need and others are satisfied by the invention, which is directed to an externally controllable circuit breaker having a set of main contacts, a set of secondary contacts, and a control mechanism for opening and closing the set of secondary contacts. The control mechanism includes an electromagnet having a coil, which is electrically interconnected with the set of main contacts for energization therefrom and adapted for control by an external signal.
In accordance with the invention, an externally controllable circuit breaker comprises a set of main contacts; an operating mechanism for opening and closing the set of main contacts; a set of secondary contacts electrically connected in series with the set of main contacts; a control mechanism for opening and closing the set of secondary contacts, the control mechanism comprises an electromagnet including an armature having a first position which opens the set of secondary contacts and having a second position which closes the set of secondary contacts, the electromagnet also including a coil electrically interconnected with the set of main contacts for energization therefrom and adapted for control by at least one external signal to operate the armature between the first position and the second position.
As another aspect of the invention, a circuit breaker comprises a set of main contacts; an operating mechanism for opening and closing the set of main contacts; a set of secondary contacts electrically connected in series with the set of main contacts; means for opening and closing the set of secondary contacts in response to at least one external signal; and means for energizing the means for opening and closing from the set of main contacts.
It is an object of the invention to provide an externally controllable circuit breaker for which external control circuitry is simple and economical to implement.